Method of and apparatus for grinding wafer

Abstract

A wafer is ground by switching between a self-sharpening-accelerated grinding step and a self-sharpening-decelerated grinding step on the basis of a load current value of a spindle motor, a loading value of grindstones, and/or the distance that the grindstones are moved. Therefore, compared to grinding the wafer only in the self-sharpening-accelerated grinding step, abrasive grains dislodged from the grindstones are reduced, and the amount of wear of the grindstones is restrained. In addition, compared to grinding the wafer only in the self-sharpening-decelerated grinding step, fluids supplied to the grindstones are saved, the time required to grind the wafer is shortened, and the processing quality of the wafer is increased. Consequently, undue wear on the grindstones is restrained while maintaining a desired level of quality of the ground surface of the wafer, resulting in a reduction in the frequency at which a grinding wheel including the grindstones is replaced.

What is claimed is: 
     
         1 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones; and   a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones,   wherein, in the self-sharpening-accelerated grinding step when a load current value of a spindle motor that rotates the grindstones while the grindstones are grinding the wafer has reached a preset first current threshold value or a predetermined first period of time has elapsed after the load current value of the spindle motor reached the preset first current threshold value, or when a loading value for pressing the grindstones against the wafer has reached a preset first loading threshold value or a predetermined second period of time has elapsed after the loading value reached the preset first loading threshold value, or when the contact surfaces of the grindstones have further been moved in a direction toward the wafer by a predetermined distance after having contacted the wafer in the self-sharpening-accelerated grinding step, the self-sharpening-accelerated grinding step transitions to the self-sharpening-decelerated grinding step.   
     
     
         2 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones; and   a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones,   wherein, in the self-sharpening-accelerated grinding step when a load current value of a spindle motor that rotates the grindstones while the grindstones are grinding the wafer has reached a preset first current threshold value or a predetermined first period of time has elapsed after the load current value of the spindle motor reached the preset first current threshold value, and when a loading value for pressing the grindstones against the wafer has reached a preset first loading threshold value or a predetermined second period of time has elapsed after the loading value reached the preset first loading threshold value, the self-sharpening-accelerated grinding step transitions to the self-sharpening-decelerated grinding step.   
     
     
         3 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones; and   a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones,   wherein, in the self-sharpening-decelerated grinding step when a load current value of a spindle motor that rotates the grindstones while the grindstones are grinding the wafer has reached a preset second current threshold value or a predetermined first period of time has elapsed after the load current value of the spindle motor reached the preset second current threshold value, or when a loading value for pressing the grindstones against the wafer has reached a preset second loading threshold value or a predetermined second period of time has elapsed after the loading value reached the preset second loading threshold value, or when the contact surfaces of the grindstones have further been moved in a direction toward the wafer by a predetermined distance after having contacted the wafer in the self-sharpening-decelerated grinding step, the self-sharpening-decelerated grinding step transitions to the self-sharpening-accelerated grinding step.   
     
     
         4 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones; and   a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones,   wherein, in the self-sharpening-decelerated grinding step when a load current value of a spindle motor that rotates the grindstones while the grindstones are grinding the wafer has reached a preset second current threshold value or a predetermined first period of time has elapsed after the load current value of the spindle motor reached the preset second current threshold value, and when a loading value for pressing the grindstones against the wafer has reached a preset second loading threshold value or a predetermined second period of time has elapsed after the loading value reached the preset second loading threshold value, the self-sharpening-decelerated grinding step transitions to the self-sharpening-accelerated grinding step.   
     
     
         5 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones while measuring a thickness of the wafer with a thickness measuring unit; and   a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer to a preset thickness with the grindstones,   wherein, when the thickness of the wafer measured by the thickness measuring unit has reached a preset first thickness threshold value, the self-sharpening-accelerated grinding step transitions to the self-sharpening-decelerated grinding step.   
     
     
         6 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones until the contact surfaces of the grindstones have further been moved in a direction toward the wafer by a predetermined distance after having contacted the wafer;   a thickness measuring step of measuring a thickness of the wafer ground in the self-sharpening-decelerated grinding step; and   a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer to a preset thickness with the grindstones; and   a regrinding step of, when the thickness measured in the thickness measuring step has not reached a preset first thickness threshold value, supplying the first fluid to the wafer and the grindstones and grinding the wafer with the grindstones until the contact surfaces of the grindstones have further been moved in the direction toward the wafer by a distance represented by a difference between the thickness measured in the thickness measuring step and the first thickness threshold value,   wherein, when the thickness measured by the thickness measuring unit has reached the preset first thickness threshold value, the self-sharpening-accelerated grinding step transitions to the self-sharpening-decelerated grinding step.   
     
     
         7 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones while measuring a thickness of the wafer with a thickness measuring unit;   a thickness measuring step of measuring a thickness of the wafer ground in the self-sharpening-decelerated grinding step; and   a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer to a preset thickness with the grindstones,   wherein, when the thickness of the wafer measured by the thickness measuring unit has reached a preset second thickness threshold value, the self-sharpening-decelerated grinding step transitions to the self-sharpening-accelerated grinding step.   
     
     
         8 . A method of grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a self-sharpening-decelerated grinding step of supplying a second fluid for decelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer with the grindstones until the contact surfaces of the grindstones have further been moved in a direction toward the wafer by a predetermined distance after having contacted the wafer;   a thickness measuring step of measuring a thickness of the wafer ground in the self-sharpening-decelerated grinding step;   a self-sharpening-accelerated grinding step of supplying a first fluid for accelerating self-sharpening of the contact surfaces of the grindstones to the wafer and the grindstones and grinding the wafer to a preset thickness with the grindstones; and   a regrinding step of, when the thickness measured in the thickness measuring step has not reached a preset second thickness threshold value, supplying the second fluid to the wafer and the grindstones and grinding the wafer with the grindstones until the contact surfaces of the grindstones have further been moved in the direction toward the wafer by a distance represented by a difference between the thickness measured in the thickness measuring step and the second thickness threshold value,   wherein, when the thickness measured by the thickness measuring unit has reached the preset second thickness threshold value, the self-sharpening-decelerated grinding step transitions to the self-sharpening-accelerated grinding step.   
     
     
         9 . The method of grinding a wafer according to  claim 1 , wherein the self-sharpening-accelerated grinding step transitions to the self-sharpening-decelerated grinding step when the load current value of the spindle motor that rotates the grindstones while the grindstones are grinding the wafer has become smaller than the preset first current threshold value or a third predetermined period of time has elapsed after the load current value of the spindle motor became smaller than the preset first current threshold value, or when the loading value for pressing the grindstones against the wafer has become smaller than the preset first loading threshold value or a fourth predetermined period of time has elapsed after the loading value became smaller than the preset first loading threshold value, or when the contact surfaces of the grindstones have further been moved in the direction toward the wafer by the predetermined distance after having contacted the wafer in the self-sharpening-accelerated grinding step. 
     
     
         10 . The method of grinding a wafer according to  claim 2 , wherein the self-sharpening-accelerated grinding step transitions to the self-sharpening-decelerated grinding step when the load current value of the spindle motor that rotates the grindstones while the grindstones are grinding the wafer has become smaller than the preset first current threshold value or a third predetermined period of time has elapsed after the load current value of the spindle motor became smaller than the preset first current threshold value, and when the loading value for pressing the grindstones against the wafer has become smaller than the preset first loading threshold value or a fourth predetermined period of time has elapsed after the loading value became smaller than the preset first loading threshold value. 
     
     
         11 . The method of grinding a wafer according to  claim 3 , wherein the self-sharpening-decelerated grinding step transitions to the self-sharpening-accelerated grinding step when the load current value of the spindle motor that rotates the grindstones while the grindstones are grinding the wafer has become larger than the preset second current threshold value or a third predetermined period of time has elapsed after the load current value of the spindle motor became larger than the preset second current threshold value, or when the loading value for pressing the grindstones against the wafer has become larger than the preset second loading threshold value or a fourth predetermined period of time has elapsed after the loading value became larger than the preset second loading threshold value, or when the contact surfaces of the grindstones have further been moved in the direction toward the wafer by the predetermined distance after having contacted the wafer in the self-sharpening-decelerated grinding step. 
     
     
         12 . The method of grinding a wafer according to  claim 4 , wherein the self-sharpening-decelerated grinding step transitions to the self-sharpening-accelerated grinding step when the load current value of the spindle motor that rotates the grindstones while the grindstones are grinding the wafer has become larger than the preset second current threshold value or a third predetermined period of time has elapsed after the load current value of the spindle motor became larger than the preset second current threshold value, and when the loading value for pressing the grindstones against the wafer has become larger than the preset second loading threshold value or a fourth predetermined period of time has elapsed after the loading value became larger than the preset second loading threshold value. 
     
     
         13 . The method of grinding a wafer according to  claim 1 ,
 wherein the first fluid includes a liquid supplied at a preset first flow rate, and   the second fluid includes a liquid supplied at a second flow rate higher than the preset first flow rate.   
     
     
         14 . The method of grinding a wafer according to  claim 1 ,
 wherein the first fluid includes air supplied at a preset third flow rate, and   the second fluid includes a liquid supplied at a preset fourth flow rate.   
     
     
         15 . The method of grinding a wafer according to  claim 1 , wherein the first fluid or the second fluid includes a mixture of a liquid and air. 
     
     
         16 . The method of grinding a wafer according to  claim 1 ,
 wherein the first fluid and the second fluid include a mixture of a liquid and air, and   the first fluid is supplied at a total flow rate as a fifth flow rate, and the second fluid is supplied at a total flow rate as a sixth flow rate higher than the fifth flow rate.   
     
     
         17 . An apparatus for grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a chuck table for holding the wafer thereon;   a grinding mechanism for grinding the wafer on the chuck table, the grinding mechanism having the grindstones and an electric motor for rotating the grindstones that are arranged in an annular array about a central axis of the annular array;   a moving mechanism for moving the chuck table and the grinding mechanism relatively toward and away from each other;   a fluid supply mechanism for selectively supplying a first fluid and a second fluid at adjustable flow rates to the wafer and the grindstones;   a load current value measuring unit for measuring a load current value of the electric motor when the electric motor rotates the grindstones; and   a controller,   wherein the controller includes
 a first controller for carrying out a control process to control the fluid supply mechanism to supply the first fluid and move the chuck table and the grindstones relatively in directions toward each other at a predetermined feed speed, thereby grinding the wafer with the grindstones, and 
 a second controller for carrying out a control process to control the fluid supply mechanism to supply the second fluid and move the chuck table and the grindstones relatively in directions toward each other at a predetermined feed speed, thereby grinding the wafer with the grindstones, 
   the control process carried out by the first controller transitions to the control process carried out by the second controller when the load current value has reached a preset first current threshold value or a predetermined first period of time has elapsed after the load current value reached the preset first current threshold value, and   the control process carried out by the second controller transitions to the control process carried out by the first controller when the load current value has reached a preset second current threshold value or a predetermined second period of time has elapsed after the load current value reached the preset second current threshold value.   
     
     
         18 . The apparatus for grinding a wafer according to  claim 17 , further comprising:
 a loading value measuring unit for measuring a loading value applied relatively to the grindstones and the wafer,   wherein the control process carried out by the first controller transitions to the control process carried out by the second controller when the loading value has reached a preset first loading threshold value or a third predetermined period of time has elapsed after the loading value has reached the preset first loading threshold value, and   the control process carried out by the second controller transitions to the control process carried out by the first controller when the loading value has reached a preset second loading threshold value or a fourth predetermined period of time has elapsed after the loading value has reached the preset second loading threshold value.   
     
     
         19 . An apparatus for grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a chuck table for holding the wafer thereon;   a grinding mechanism for grinding the wafer on the chuck table, the grinding mechanism having the grindstones and an electric motor for rotating the grindstones that are arranged in an annular array about a central axis of the annular array;   a moving mechanism for moving the chuck table and the grinding mechanism relatively toward and away from each other;   a fluid supply mechanism for selectively supplying a first fluid and a second fluid at adjustable flow rates to the wafer and the grindstones, and   a controller,   wherein the controller includes
 a first controller for carrying out a control process to control the fluid supply mechanism to supply the first fluid and move the chuck table and the grindstones relatively in directions toward each other at a predetermined first feed speed, thereby grinding the wafer with the grindstones, and 
 a second controller for carrying out a control process to control the fluid supply mechanism to supply the second fluid and move the chuck table and the grindstones relatively in directions toward each other at a predetermined second feed speed, thereby grinding the wafer with the grindstones, and 
   the control process carried out by the first controller transitions to the control process carried out by the second controller or the control process carried out by the second controller transitions to the control process carried out by the first controller when the contact surfaces of the grindstones have further been moved in a direction toward the wafer by a predetermined distance after having contacted the wafer.   
     
     
         20 . An apparatus for grinding a wafer with contact surfaces of grindstones that are rotated, comprising:
 a chuck table for holding the wafer thereon;   a grinding mechanism for grinding the wafer on the chuck table, the grinding mechanism having the grindstones and an electric motor for rotating the grindstones that are arranged in an annular array about a central axis of the annular array;   a moving mechanism for moving the chuck table and the grinding mechanism relatively toward and away from each other;   a fluid supply mechanism for selectively supplying a first fluid and a second fluid at adjustable flow rates to the wafer and the grindstones;   a load current value measuring unit for measuring a load current value of the electric motor when the electric motor rotates the grindstones;   a loading value measuring unit for measuring a loading value applied relatively to the grindstones and the wafer; and   a controller,   wherein the controller includes
 a first controller for carrying out a control process to control the fluid supply mechanism to supply the first fluid and move the chuck table and the grindstones relatively in directions toward each other at a predetermined first feed speed, thereby grinding the wafer with the grindstones, and 
 a second controller for carrying out a control process to control the fluid supply mechanism to supply the second fluid and move the chuck table and the grindstones relatively in directions toward each other at a predetermined second feed speed, thereby grinding the wafer with the grindstones, 
   the control process carried out by the first controller transitions to the control process carried out by the second controller when the load current value has reached a preset first current threshold value or a predetermined first period of time has elapsed after the load current value reached the preset first current threshold value, and when the loading value has reached a preset first loading threshold value or a predetermined second period of time has elapsed after the loading value reached the preset first loading threshold value, and   the control process carried out by the second controller transitions to the control process carried out by the first controller when the load current value has reached a preset second current threshold value or a predetermined third period of time has elapsed after the load current value reached the preset second current threshold value, and when the loading value has reached a preset second loading threshold value or a predetermined fourth period of time has elapsed after the loading value reached the preset second loading threshold value.   
     
     
         21 . The apparatus for grinding a wafer according to  claim 17 , further comprising:
 a thickness measuring unit for measuring a thickness of the wafer held on the chuck table,   wherein the control process carried out by the first controller also transitions to the control process carried out by the second controller when the thickness of the wafer measured by the thickness measuring unit has reached a preset first thickness threshold value, and   the control process carried out by the second controller also transitions to the control process carried out by the first controller when the thickness of the wafer measured by the thickness measuring unit has reached a preset second thickness threshold value.